While what George says is true about proper DuraSpark II cars in the yards, they are indeed harder to come by...... trucks are numerous and plentiful!!!! So if you have a DIY bone in ya, you can find nice harnesses in trucks that may have some extra length in them too! But splicing to lengthen or shorten should be allowed for.... I think I had to add about 4ft to the harness that I found, out of an AMC postal truck! (AMC shared Ford parts suppliers sometimes....for a while anyway! My blue strain relief module says AMC on it, but carries a Motorcraft casting and D8TE stamping in it! (1978 Truck part..))
Also I noticed lots of old Lincolns hitting the yards lately too. They are also good sources of 429/460 distributors and modules! Many times less miles on these cars...they die more of lack of use....
Steve